Small pilot study of Hydroxyurea (HU) in children to provide preliminary data for use in designing a larger pediatric trial, if and when the clinical efficacy of HU is demonstrated in adults. Specific aims are to see if HU elevates the concentration of fetal hemoglobin (HBF), hematocrit and red cell mean corpuscular volume (MCV) in pediatric patients with sickle cell anemia, to see if maximum tolerated dose and hematologic and other toxicities of HU in pediatric patients is similar to adults. Usage is only with patients with no clear alternative therapeutic option.